The dream to inherit from a struct in c#

Question

There I am making a 2D game in C# XNA 4.0, and run across yet again a petty annoyance of mine; the Rectangle. For those using basic collision, this is almost a necessity. For almost any game object created you need to have a rectangle. Then I go to change the X, check collision, or anything else. And there I begin the never-ending battle of objectName.Rectangle.Whatever. To get around this I of course give the class of objectName properties/methods that access these for me.

Then I dared to dream. I had grand designs to make a basic game object class that everything drawable would inherit from, that would allow parenting, precise local coordinates (floats), and hold the texture/spritebatch. To make this complete I was ready to inherit from Rectangle, to use all the methods and attributes that it holds. Heck, whenever something required a Rectangle, I could be so lazy as to say objectName, not objectName.Rectangle.

Then I realized, not a chance. I started out depressed as my oh-so-clever idea was smashed to bits. Since then my perfect little class holds a rectangle, with various methods and properties accessing it as needed. I have also taken the chance to have it inherit from the XNA DrawableGameComponent. While in the long run this has been more practical, every time I view a draw or update method and see the call to rectangle I often wonder, was there ever a hope to do what I had wanted? Was there some clever work around that I could have done? Or was inheriting from a Rectangle truly sealed from my grasp?

While using the DrawableGameComponent class provided in XNA allows most game-object related actions happen inside the classes Update() method, every time outside of a class I need to reference not to property of a Rectangle, but rather the Rectangle itself, I am slightly peeved considering that in really every way my object is, in fact, and souped-up Rectangle. And then once again I can find myself asking:

Is there any way to inherit from a pre-defined struct, or give the project the impression you are (a work-around)?

Answer 1

Inherit no, but you can add a lot of 'default' functionality to the Rectangle object with extension methods. For example

  //(inside a static class)
  public static int GetSurface(this Rectangle rect){return rect.Width * rect.Height;}

  //calling
  Rectangle rect;
  var s = rect.GetSurface();

---

That said, what I normally do is encapsulate said struct. Use that class as the base object, and add an operator so that it can be implicitly cast to a Rectangle. That way it can be passed to a method that needs a rectangle without casting.

    public class MyRect //class so you can inherit from it, but you could make your own struct as well
    {
        public int X { get; set; }
        public int Y { get; set; }
        public int Width { get; set; }
        public int Height { get; set; }
        public int Right { get { return X + Width; } }
        public int Bottom{ get { return Y + Height; } }

        public static implicit operator Rectangle(MyRect rect)
        {
            return new Rectangle(rect.X, rect.Y, rect.Width, rect.Height);
        }

        public static implicit operator MyRect(Rectangle rect)
        {
            return new MyRect { X = rect.X, Y = rect.Y, Width = rect.Width, Height = rect.Height };
        }

    }       
 }

Now you can create your own rect manually or from an existing one:

  MyRect rect = ARectangleVar

And you can use it in legacy methods that expect a Rectangle without casting

Answer 2

Here's a possible workaround (put this in MyClass, the class you speak of that has a Rectangle property):

public static implicit operator Rectangle(MyClass obj)
{
    return obj.Rectangle;
}

This will, e.g. allow you to pass your object to a method expecting a Rectangle, and it work. Note that unlike with true inheritance, the Rectangle that exists isn't the same instance of MyClass that you passed in, it's just a struct made from the value.